Electrostatic spray guns used for charging particles of a coating material emitted from the gun are well known. To attract the coating material to the article to be covered, the coating particles are charged to the opposite polarity of the article to be coated. Early forms of electrostatic spray guns were powered from remote high-voltage dc supplies that provided output voltages of 70 kilovolts (KV) or higher. The output voltage of such power supplies was conducted via high voltage cables to particle-charging electrodes mounted proximate the nozzles of the guns. These high voltage cables typically were stiff, making the gun difficult to maneuver, and stored potentially dangerous levels of electrical energy which created shock and ignition hazards.
To provide a safer and more maneuverable gun, miniaturized voltage multiplier circuits operating at high frequency were developed that could fit within the electrostatic spray gun to produce the requisite high dc charging voltage from a relatively low input voltage. Such guns with internal high voltage multiplication capabilities are generally powered from either an external low voltage power supply via a low voltage cable to the gun which is more flexible than high voltage cables, or a low voltage power supply, such as a battery, located within the gun which eliminates a cable altogether. The internal high voltage circuit steps up the low input voltage by means of a transformer, rectifies and multiplies the stepped-up voltage in a diode/capacitor multiplier cascade, and outputs a high dc voltage to the particle-charging electrode of the gun.
Electrostatic guns with internal voltage multiplier circuits are particularly advantageous for manual spray coating applications since the guns are more maneuverable than guns supplied from external high voltage power supplies having stiff and bulky high voltage cables. However, maneuverability is not generally a consideration in applications where the gun is robot-controlled or machine-reciprocated, and as a consequence in such installations it is common to use external high voltage power supplies.
Historically, electrostatic spray gun manufacturers marketing both manual and robot-controlled or machine-reciprocated guns had to manufacture guns of entirely different construction for these two different applications. The additional tooling and parts inventory required to support the manufacture of two different gun constructions unnecessarily increased the cost of gun manufacture.